A In general, foods that need to be chilled (which include most of the foods people tend to serve on buffets and most sandwich fillings) should be left out of the fridge for the shortest time possible.

If they are left at room temperature for a long time, bacteria can grow or toxins can form, and both of these could cause food poisoning. If you are preparing a buffet at home for friends or family, there aren't any regulations that specify a maximum time that food can be left out but, in the interests of safety, you should try and keep it short (not more than four hours). Then any remaining food should be thrown away or put back in the fridge. If you keep leftovers in the fridge, don't let them stand around at room temperature when you serve them again.

However, if you are preparing a buffet (or any other food) as part of a business, which in some circumstances could include charitable or community events, you must follow food safety regulations. The law requires caterers to keep certain foods at specified temperatures for food safety reasons.

Chilled foods must be kept at or below 8 C, while foods that are being kept hot before serving should remain at or above 63 C. Contact the environmental health service at your local authority for more information on what regulations apply to you.

The law allows food to be left at room temperature for limited periods during service or when on display. The temperature of chilled foods can exceed 8 C for up to four hours, while the temperature of hot foods can fall below 63 C for a maximum of two hours. However, these flexibilities can be used only once for each batch of food. In other words, the same food can't be left out at room temperature for more than one period. After one period at room temperature, food should be thrown away or chilled until final use.

Sam Montel is the Food Standards Agency's online nutrition expert and a registered public health nutritionist.

She will be answering a different question about healthy eating every week. To find out more about food, visit the Food Standards Agency's